docs: def _worker_thread_transfer(self):
          # type: (SyncCopy) -> None
          """Worker thread download
          :param SyncCopy self: this
          """
          while not self.termination_check:
              try:
                  sd = self._transfer_queue.get(block=False, timeout=0.1)
              except queue.Empty:
                  continue
              try:
                  self._process_synccopy_descriptor(sd)
              except Exception as e:
                  with self._transfer_lock:
                      self._exceptions.append(e)